“We let go after an avoidable second goal and should’ve stayed in the shape we prepared before the game, but were naïve,” he told Rai Sport.

Juve scored three goals between the 53rd and 56th minutes, finding the net with Giorgio Chiellini, Carlos Tevez and Stephan Lichtsteiner after Paul Pogba’s first half opener.

“It was a psychological collapse and with that black-out we conceded another two goals in quick succession.

“Juve didn’t create much until the second goal. We conceded an avoidable goal from a dubious free kick and Juventus were smart. They deserve credit for that.

“We certainly have to get our feet back on the ground. We tried to do that after winning the Coppa Italia Final and must do it again now. We were perhaps a little too confident against a great Juve side when we weren’t 100 per cent fit.

“We have to take a good look at ourselves and recognise our mistakes, starting from myself, because for us this new journey begins today. Even after defeats like this we have to show our character and how to get back on track.

“It’s always tough to lose by more than two goals, but we will be ready for the first game of the Serie A season against Udinese.”

Sergio Floccari was a surprisingly late substitute and Petkovic explained his approach.

“It was a very balanced game that only an incident could turn. I was waiting for the right moment to introduce Floccari, but then this black-out happened.

“We apologise to the fans and the city. We turn over a new leaf and move forward.”